This is silly. If the head is returned to the upright position, the missile channel is going to move, as HSCA exhibit F-46 shows. With the head upright, the bullet would have exited with an upward trajectory.
But, of course, this is all academic anyway, because we now know that the back wound had no exit point, and that the front shirt slits and the nick on the tie were made by the nurses, not by a bullet.
Yes, Dr. Carrico told Harold Weisberg that the slits in the front of the shirt and the nick on the tie were caused by the scalpels of the nurses cutting the clothes off, under his personal supervision. And the FBI found no copper residue on those slits, but the holes in the back of the shirt and suit jacket did contain traces of copper.
Dr. Carrico testified under oath that the wound in the anterior neck was located above the collar of the shirt.
Agents Francis X. O’Neill, Jr. and James W. Sibert attended the autopsy and wrote a report, which for some reason wasn't included in the Warren Commission's volumes. THey wrote:
During the latter stages of this autopsy, Dr. Humes located an opening which appeared to be a bullet hole which was below the shoulders and two inches to the right of the middle line of the spinal column. This opening was probed by Dr. Humes with the finger, at which time it was determined that the trajectory of the missile entering at this point had entered at a downward position of 45 to 60 degrees. Further probing determined that the distance travelled by this missile was a short distance inasmuch as the end of the opening could be felt with the finger.This angle of 45 degrees also popped up during Assistent Counsel Arlen Specter's questioning of the Parkland doctors:
"Permit me to add some facts which I shall ask you to assume as being true for purposes of having you express an opinion.
First of all, assume that the President was struck by a 6.5 mm. copper-jacketed bullet from a rifle having a muzzle velocity of approximately 2,000 feet per second at a time when the President was approximately 160 to 250 feet from the weapon, with the President being struck from the rear at a downward angle of approximately 45 degrees, being struck on the upper right posterior thorax just above the upper border of the scapula 14 centimeters from the tip of the right acromion process and 14 centimeters below the tip of the right mastoid process."
How did a downward angle of 45 degrees change to an upward angle of some 25 degrees as per the HSCA?